Breathable elastomeric composites with tether-containing conducting polymers for nanoscale diffusion control and protection

ABSTRACT

An interpenetrating network (IPN) polymer membrane material includes a soft polyurethane interspersed with a crosslinked conducting polymer. The material can be reversibly “switched” between its oxidized and reduced states by the application of a small voltage, ˜1 to 4 volts, thus modulating its diffusivity.

CROSS-REFERENCE TO RELATED APPLICATIONS

This Application is related to U.S. Pat. Nos. 8,120,893 and 8,931,114.

BACKGROUND

New materials having nanoscale porosities that can be reversibly changedon command are of great interest in a variety of applications. In thearea of chemical threat protection, they may have a major impact.

BRIEF SUMMARY

In one embodiment, a conductive polymer comprisespoly(TP-CAE4P-SO3-co-bis-EDOT-co-HM-EDOT.

In another embodiment, a material comprises an interpenetrating polymernetwork comprisingnet-(poly(TP-CAE₄P—SO₃-co-bis-EDOT-co-HM-EDOT)-co-(net-(poly(propyleneglycol-tolylene 2,4 diisocyanate)))-ipn-(polyurethane).

In a further embodiment, a method of modulating the diffusivity of amaterial includes reducing the material to decrease its diffusivity andoxidizing the material to increase its diffusivity, wherein the materialcomprises a conductive polymer comprisingpoly(TP-CAE4P-SO3-co-bis-EDOT-co-HM-EDOT).

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 depicts the electroactive open-close behavior of the IPN.

FIG. 2 shows the termonomers used in the synthesis of thetether-containing conducting polymer.

FIG. 3 illustrates an exemplary synthesis ofpoly(TP-CAE₄P—SO₃-co-bis-EDOT-co-HM-EDOT).

FIG. 4 depicts resistance of the conducting polymer as a function of theinverse of the perturbation frequency.

FIG. 5 provides the structure of the poly(propylene glycol-tolylene 2,4diisocyanate) crosslinker.

FIG. 6 shows IPN composition.

FIG. 7 displays the structure of IPNnet-(poly(TP-CAE₄P—SO₃-co-bis-EDOT-co-HM-EDOT)-co-(poly(propyleneglycol-tolylene 2,4 diisocyanate)))-ipn-(net-(polyurethane)), termed“IPN 1”.

FIG. 8 illustrates the role of tether in the formation of the IPN closedprotective state.

FIG. 9 is a schematic showing the electroactuation of IPN and formationof closed state, with the fabric IPN support not shown.

FIG. 10 shows an example of the current flow between the top and bottomelectrodes as a reducing voltage bias of −2.0 V is applied to transformthe composite into its closed protective state.

FIG. 11 is a plot of resistance vs. the inverse of the perturbationfrequencies used in the impedance spectroscopy, which depicts thedecreases in composite resistance as the IPN is switched from its openstate (45 Ohms) to the closed state (15.5 Ohms).

FIGS. 12 and 13 show the syntheses of conducting polymers A and B,respectively.

FIG. 14 illustrates the structures of conducting polymers A, B, and C.

FIG. 15 shows the resistances of conducting polymers A, B, and C.

FIG. 16 illustrates the synthesis of IPN 2.

FIG. 17 illustrates the synthesis of IPN 3.

FIG. 18 shows the structure of IPNs 1 through 3.

FIGS. 19 and 20 indicate resistances of the open and closed states ofIPN 2-fabric composite and IPN 3-fabric composite, respectively.

FIG. 21 shows the standard testing cell for measurement of vaporpermeation rates through solid samples.

FIG. 22 is a schematic of a testing cell showing the nitrogen carrierstream.

FIG. 23 shows data measured by a flame-ionization detector (FID) forpassage of simulant through the cell with no sample present in thegasket (black trace, representing 2.3 mg of simulant vapor), and passagethrough the open state of the IPN 1—fabric composite.

FIG. 24 provides data for passage of the simulant through the open andclosed state of the IPN 1—fabric composite.

FIG. 25 shows data for simulant passage through the Zorflex® fabricalone, and passage through the IPN 1-fabric composite closed state.

FIG. 26 shows simulant passage through the IPN 1-fabric composite closedstate after 48 hours (red) and 7 days (black).

FIG. 27 summarizes the amounts of simulant that were passed by variousstates of the composite at four time intervals, and the open gasket.

FIG. 28 is a comparison of simulant passage through IPN-fabriccomposites 1-3.

FIG. 29 shows vapor transport rates through IPN-fabric composites at 37°C., 50% relative humidity.

FIG. 30 indicates moisture vapor transport rates through IPN 1-fabriccomposites at 37° C., as a function of relative humidity.

FIG. 31 shows data for vapor passage by the HC—IPN 1-fabric composite.

FIG. 32 depicts moisture vapor transport rates through the IPN 1-fabriccomposites and the HC—IPN 1-fabric composite at 37° C., as a function ofrelative humidity.

DETAILED DESCRIPTION Definitions

Before describing the present invention in detail, it is to beunderstood that the terminology used in the specification is for thepurpose of describing particular embodiments, and is not necessarilyintended to be limiting. Although many methods, structures and materialssimilar, modified, or equivalent to those described herein can be usedin the practice of the present invention without undue experimentation,the preferred methods, structures and materials are described herein. Indescribing and claiming the present invention, the following terminologywill be used in accordance with the definitions set out below.

As used herein, the singular forms “a”, “an,” and “the” do not precludeplural referents, unless the content clearly dictates otherwise.

As used herein, the term “and/or” includes any and all combinations ofone or more of the associated listed items.

As used herein, the term “about” when used in conjunction with a statednumerical value or range denotes somewhat more or somewhat less than thestated value or range, to within a range of ±10% of that stated.

Overview

Described herein is an interpenetrating network (IPN) polymer membranematerial composed of soft polyurethane interspersed with a crosslinkedconducting polymer. The material can be reversibly “switched” betweenits oxidized and reduced states by the application of a small voltage,˜1 to 4 volts. The conducting polymer network contains molecular tethersthat each have a charged terminus. When the network is “switched,” thepolymer chain morphology is altered and the moveable tethers formion-pairing complexes that either increase or decrease the material'snanoporosity. The material thus has an “open” state that has arelatively high porosity, and a “closed” state with a lowered porosity.Chemical protective clothing, or clothing sections, formed from it willhave a high permeability to water vapor in the open state. This providesbreathability and is thus comfortable for the wearer, and physicalactivity can be performed easily. However, if a chemical agent appears,application of the small voltage will rapidly “switch” the material tothe closed state. When closed, the clothing will block or greatlydiminish transport of the agent, as seen in FIG. 1. The closed state hasa large degree of bistability—it is maintained for a period of dayswithout need for voltage application.

The interpenetrating network (IPN) can be formed, with good adhesion, incommon support fabrics such as wool or cotton/nylon. It can also beformed in commercially available electrically conducting fabrics such asthose based on nanoporous absorptive carbon fibers or carbon nanotubes.The conducting fabrics enhance the switching ability of the IPN. Also,they can serve as a platform for wearable warfighter electronics such assensors and communication devices.

When challenged with simulant vapor, the closed state IPN is able toblock 99% of the vapor amount that had passed through while in an openstate. When challenged again after three days, its performance wasnearly identical. Thus the closed IPN is bistable for operationallysignificant time periods. The open state of the material has shown veryhigh breathabilities, in terms of moisture vapor transport (gramswater/square meter per day), that meets or exceeds those of state of theart commercial sport clothing. Also, at relative humidity of up to 50%,the closed state demonstrates a substantial breathability as well, morethan one-half of that shown by the open state.

By casting a polymer solution the IPN can be formed within fabrics. Thisis expected to allow straight-forward manufacture and scale-up. The IPNforms through chemical crosslinking processes that occur when thesolution is deposited. Use of selected solvents at moderate temperatureswill allow other CB protective elements, for example an agent-degradingenzyme, to be introduced into the IPN during its formation

IPN Synthesis

FIG. 2 shows the termonomers used in the synthesis of thetether-containing conducting polymer, which is depicted in blue in FIG.1.

In FIG. 2, the proper chemical name for termonomer (a) is(3-{2-[2-(2-{2-[(thiophene-3-carbonyl)-amino]-ethoxy}-ethoxy)-ethoxy]-ethoxy}-propane-1-sulfonicacid). It will be referred to as “TP-CAE₄P—SO₃”. Termonomer (b), whichis 5, 5 bis-3,4 ethylenedioxythiophene, will be referred to as“bis-EDOT”, and termonomer c), which is hydroxymethyl-3,4ethylenedioxythiophene, will be referred to as “HM-EDOT”.

Poly(TP-CAE₄P—SO₃-co-bis-EDOT-co-HM-EDOT) was synthesized by dissolving700 mg of TP-CAE₅-SO₃ in 12.5 mL deionized water while heating to 75° C.in an oven for 15 minutes. Next, 325 mg of bis-EDOT and 75 mg of HM-EDOTwere dissolved in 12.5 ml of N-methyl pyrrolidone while heating to 75°C. in an oven for 15 minutes. The two mixtures were then mixed, whilevigorous blending took place for 2 minutes at 87° C., with theassistance of a magnetic stir bar/stir plate. Finally, 3.5 grams ofammonium cerium nitrate (98.5% purity) was added to the mixture, whichwas allowed to continue to stir, and the reaction was allowed to proceedfor 2 hours at 87° C. (FIG. 3). The reaction was then stopped, andallowed to cool to room temperature. The polymer product wasprecipitated from the solution by adding 50 mL of deionized water. Afterprecipitation, the supernatant was decanted and the polymer was driedovernight under nitrogen at 87° C. to remove residual solvent.

FIG. 4 shows the resistance of the conducting polymer as a function ofthe inverse of the perturbation frequency, as measured byelectrochemical impedance spectroscopy. The slope of the plot isinversely related to the value of the ion diffusion coefficient in thematerial—the shallower the slope, the faster the ions move, and the morethey contribute to the bulk conductivity of the material. From FIG. 4 itis seen that the average resistance of the polymer, coated as a thinfilm on a platinum electrode, is roughly 1000 Ohms.

The IPN was synthesized by blending the conducting polymer with thepolyurethane support polymer, and adding a long-chain flexiblediisocyanate to crosslink the conducting polymer chains through thehydroxyl group present in the HM-EDOT. For this purpose, the polarsolvent N-methyl pyrrolidone was used. A third component, conductingcarbon fibers (˜50 microns in length) was added into the blend to act asan electron donor in the final IPN material. The blend was then castinto a support fabric such as cotton/nylon, wool, or carbon cloth thatis electrically conducting. Typically, the casting was done to result inan IPN-fabric composite material having a weight ratio between 1 to 1and 2 to 1. After the casting solvent dried, the formed IPN was found tobe very adherent to the fabric and exhibited a high conductivity. Thefinal component of the IPN, an ionic liquid, was then added in arelatively small amount (5 to 10 wt %). Its purpose was to assist incharge balance during the electroactive process that occurs in thepolymer as it is switched into its closed state.

For preparation of a typical IPN formation, 100 mgpoly(TP-CAE₄P—SO₃-co-bis-EDOT-co-HM-EDOT) was added to 1.0 mL N-methylpyrrolidone containing 5 wt % dissolved polyurethane (50 mg, trade nameMVT 75®, originally manufactured by BF Goodrich). Next, 20 mg choppedcarbon (graphite) fibers (trade name Granoc®, manufactured by NipponGraphite Fiber Corporation) were added. The mixture was then blendedvigorously for 20 minutes using a magnetic stir bar/stir plate (stirringrate ˜1000 rpm). Next, 10 mg of the long-chain crosslinkerpoly(propylene glycol-tolylene 2,4 diisocyanate) (FIG. 5) was added tothe solution, followed by 1.0 mg of the catalyst iron(III)acetylacetoneate. The mixture was immediately stirred for 1 minute usinga magnetic stir bar/stir plate (stirring rate ˜500 rpm). Finally, themixture was cast onto conducting carbon fabric (Zorflex®, manufacturedby Calgon, Inc.) having an area of 2 cm×2 cm, and a weight of ˜80 mg.The fabric was pre-heated to 80° C. in an oven, and the curing processwas allowed to proceed in the oven at 80° C. overnight under nitrogenflow. The resulting IPN-fabric composite was found to have a weight of160 mg, and an IPN-fabric weight ratio of 2:1.

The synthesis was furthered by adding 8 microliters of the ionic liquid(IL) 1-butyl-3-methyl imidazolium tetrafluoroborate, blended into anethanol carrier in an amount of 33 wt %. Specifically, 10 microliters ofIL was added to 20 microliters ethanol, and mixed thoroughly. Next, 24microliters of this solution was added dropwise to the IPN-fabriccomposite, with care being taken to ensure an even distribution acrossthe fabric. The composite was then allowed to dry overnight beforefurther characterization was undertaken.

The composition of the IPN is depicted in FIG. 6. The IUPAC designationof its polymeric structure isnet-(poly(TP-CAE₄P—SO₃-co-bis-EDOT-co-HM-EDOT)-co-(net-(poly(propyleneglycol-tolylene 2,4 diisocyanate)))-ipn-(polyurethane). It will bereferred to as “IPN 1”. The polymer structure is shown in FIG. 7. Thecountercation for the tethered sulfonate is either sodium or ammoniumion.

Theory of IPN Electroactuation from Open to Closed State

In this model, the electroactive IPN is able to generate a closed,protective state via charge rearrangement that causes a change in thephysical properties of the conducting polymer (CP) component. In itsopen, breathable state the CP is oxidized, polycationic and mechanicallyrelatively rigid.

The negatively-charged tethers attached to the CP main chain form ionpairs either with the cationic centers in the main chain, or withcationic centers on neighboring CP chains. Either configurationcontributes to a mechanically rigid structure with an open nanoporositythat is conducive to high moisture vapor transport (MVT) rates. Whenelectrons are added into the IPN—when it is reduced—the cationic centersin the CP main chain are neutralized, and the negatively-charged tethersare released. The neutralized CP main chains experience attractiveforces due to pi-pi interactions between the now-aromatic repeat unitsand aggregate. This increases the density of the IPN, and results in theprotective closed state.

The source of the reducing electrons, which are carbon fibers in anotherregion of the IPN, now contain cationic centers themselves. These areneutralized by the ionic liquid anions. Simultaneously, ionic liquidcations pair with the freed negatively-charged tethers to maintaincharge balance.

This process is driven by a voltage bias that is applied between aworking and counter electrode. The electrodes may be placed in asandwich configuration in which the IPN-fabric composite is placed inthe center, or in a parallel configuration in which both electrodes areplaced on top of the IPN fabric composite. The voltage bias rangesbetween −1 and −4 volts and results in reduction at the workingelectrode with oxidation at the counterelectrode. A DC power supply isused to generate the bias.

FIG. 8, a detailed version of FIG. 1, depicts the IPN with its CP andpolyurethane components. The oxidized state of the CP, which yields theopen state of the IPN, is shown in blue. The negatively charged tethersare shown in an intramolecular ion-pairing configuration. When the CP isreduced (now shown in red), the tethers are released, exposing the CPmain chains to one another, and allowing them to aggregate via pi-piinteractions. This causes a localized increase in IPN density whichresults in the protective closed state.

FIG. 9 shows the IPN-fabric in a sandwich configuration between aworking and counter electrode. Both electrodes are constructed fromporous conducting carbon cloth (such as Zorflex®), which is readilycommercially available. The porosity allows the cloth to have a highMVT. This Figure depicts the switching of the IPN into its closed state,in the top region of the IPN-fabric, and the resulting charge balancingthat is undertaken by the ionic liquid component.

Results from IPN Electroactuation

FIG. 10 shows an example of the current flow between the top and bottomelectrodes as a reducing voltage bias of −2.0 V is applied to transformthe composite into its closed or protective state. In this case, 3.50Coulombs of charge passes during the time duration of the voltageapplication. The steady increase of the current level indicates that theconductivity of the composite increases as the IPN is reduced. FIG. 11,a plot of resistance vs. the inverse of the perturbation frequenciesused in the impedance spectroscopy, depicts the decreases in compositeresistance as the IPN is switched from its open state (45 Ohms) to theclosed state (15.5 Ohms). The conductivity increase may arise frompi-stacking of the CP chains. The resistance of the uncoated Zorflex®(469 Ohms) is shown also. As discussed below, the horizontal nature ofthe plots indicate that ion diffusion processes in the composite arerelatively very fast.

In terms of general parameters, to transform the material into itsclosed state, the voltage bias used ranged from −1 to −5 volts, thecurrent ranged from 0.005 to 0.24 amps, the charge passage ranged from0.20 to 14 Coulombs, and the time of voltage application ranged from 10to 180 seconds.

Synthesis of Comparative Conducting Polymers and IPNs

In a typical synthesis of conducting polymer A (depicted in FIG. 12),1.6 mL anisole containing 60 mg EDOT-ODA-EDOT and 40 μL EDOT was addedto 1.4 mL ethanol containing 240 mg TP-CAE₄P—SO₃. This mixture was thenadded to 2.0 mL ethanol containing 1.2 g iron (III) tosylate hexahydrateoxidant, and the blend was mixed vigorously for 5 minutes at roomtemperature. The solution was then cast into 8 cm² of wool fabric, whichwas then heated at 75° C. overnight in an oven. The resulting conductingpolymer-fabric composite had a polymer-fabric weight ratio of 2 to 1.The residual iron (II) salts were removed by immersion of the compositein hot water (80° C.) and agitation for one minute. The composite waspermitted to dry for 4 hours at 75° C., and its electrical resistancewas then characterized using electrical impedance spectroscopy.

In a typical synthesis of conducting polymer B (depicted in FIG. 13),3.0 mL N-methyl pyrrolidone (NMP) containing 150 mg TP-CAE₄P-SO₃, 15 μL3,4 ethylenedioxythiophene (EDOT), and 36 mg HM-EDOT was added to 3.0 mLN-methyl pyrrolidone. Next, 240 mg iron (III) chloride was added and thereaction was performed at 60 C for 1 hour. The NMP solvent was removedat 60° C. overnight under vacuum provided by a vacuum pump. The dryproduct was then washed with methanol three times to remove the iron(II) byproduct. The final product poly(TP-CAE₄P—SO₃-co-EDOT-co-HM-EDOT)could be re-dissolved in NMP for characterization using electricalimpedance spectroscopy.

Synthesis of polymer C of the present invention, namelypoly(TP-CAE₄P—SO₃-co-bis-EDOT-co-HM-EDOT), was described at above.

The structures of conducting polymers A, B, and C are provided in FIG.14. It can be seen that a primary difference among them that thebis-EDOT moiety is present in the polymer C but the other two containonly singular EDOT units. This contributes to a regioregularity in thelatter that likely contributes to a higher conductivity as is seen inFIG. 15, which shows that polymer A has an average resistance of ˜4500Ohms, polymer B has a resistance of ˜6300 Ohms, and polymer C having thelowest, ˜1000 Ohms. It was anticipated that lower polymer resistancewill contribute to greater IPN electroactivity and the creation of themost effective IPN closed protective states.

To form IPN 2, 10 mg of conducting polymer B was blended into 0.1 mL ofa 5 wt % polyurethane—NMP solution, followed by blending addition of 2mg carbon fibers, 1.5 mg poly(isocyanate) manufactured by Bayer Ltd.(Bayhydur®), and 0.5 mg iron (III) acetylacetonate.

The solution was then divided into two parts of equal volume, and castinto two samples of polyester fabric of dimensions 1.25 cm×1.75 cm each(FIG. 16). Each polyester sample weighed 20 mg before the casting. EachIPN-fabric sample was allowed to cure overnight at 78° C. The next day,the samples were subjected to an identical casting, except that anadditional 0.05 mL NMP was added to the 0.1 mL NMP-polyurethanesolution, and then the other components were added. This dilutionresulted in an improved dispersion and solvation of the components. Thesecond casting resulted in IPN-fabric composites having the followingweight percentage of each component—52 wt % fabric support, and 48 wt %crosslinked IPN. The IPN consisted of 54 wt % conducting polymer, 27 wt% polyurethane, 11 wt % carbon fibers, and 8 wt % polyisocyanate. Thesamples were then briefly washed with DI water to remove iron saltsoriginating from the iron (III) acetylacetonate catalyst. The ionicliquid 1-ethyl-3-methyl imidazolium-bis-(perfluoroethylsulfonyl) imidewas then added into the IPN (via 30% solution in ethanol), to give afinal concentration of 9 wt % (ethanol fraction assumed evaporated). Atthis point the composition of the IPN was 49 wt % conducting polymer, 25wt % polyurethane, 10 wt % carbon fibers, 9 wt % ionic liquid and 7 wt %polyisocyanate.

In a typical synthesis of IPN 3, 1.7 mL of THF containing 10 wt %polyurethane was and 50 mg chopped carbon fibers was added to 1.6 mLanisole containing 60 mg EDOT-ODA-EDOT. Next, 40 μL EDOT was added to1.4 mL ethanol containing 240 mg TP-CAE₄P—SO₃. This mixture was thenadded to 2.0 mL ethanol containing 1.2 g iron (III) tosylate hexahydrateoxidant, and the blend was mixed vigorously for 20 minutes at roomtemperature. The solution was then cast into 14 cm2 of wool fabric,which was then heated at 75° C. overnight in an oven (FIG. 17). Theresulting IPN-fabric composite had an IPN-fabric weight ratio of 2 to 1.The residual iron (II) salts were removed by immersion of the compositein hot water (80° C.) and agitation for one minute. The composite waspermitted to dry for 4 hours at 75° C., and its electrical resistancewas then characterized using electrical impedance spectroscopy. Thestructures of IPNs I through III are given in FIG. 18.

Electroactuation of Comparative IPNs

The IPNs 2 and 3 were switched into their closed, protective state byapplication of a small negative voltage bias, usually between 1 and 2.5volts (see Theory of IPN Electroactuation from Open to Closed State,above) for time periods normally ranging from 30 to 180 seconds. Sincethe actuation causes a chemical change and rearrangement of the polymerchains, the conductivity of the composites changes, increasing as thematerial is transformed into its closed state. The resistance of thematerials in their open and closed states is depicted in FIGS. 19-20.

Characterization of Comparative IPNs

A standard testing cell for measurement of vapor permeation ratesthrough a solid sample is shown in FIG. 21. The sample, for example afabric, is attached to a circular metal support that is then placedinside the stainless steel chamber, sealed with a rubber gasket. A smalldrop of liquid simulant is placed near the sample, and the top of thechamber is then threaded into place. The cell is then mounted to atubing system that provides a steady stream of nitrogen gas, which isdirected past the lower side of the sample. The simulant droplet ispermitted to slowly evaporate, and any simulant vapor that passesthrough the sample is absorbed into the nitrogen stream and carried intoa flame-ionization detector (FIG. 22). This allows the amount ofsimulant that passed through the sample to be quantified as a functionof time.

Typical detection vs. time traces for the IPN 1—fabric composite areshown in FIGS. 23-26, for a testing time of 900 minutes at 25° C., using50% relative humidity in the nitrogen carrier stream. The first plot(FIG. 23) shows the passage of the simulant dimethyl methyl phosphatethrough the cell with no sample present in the gasket (black trace,representing 2.3 mg of simulant vapor), and passage of the vapor throughthe open state of IPN 1 supported by the conducting fabric Zorflex® (redtrace, see above). Integration of both traces shows that the open stateof the IPN-fabric composite allowed passage of 81% of the vapor amountthat passes through the open gasket (no vapor present). FIG. 24 depictsthe passage of the vapor through the closed state of IPN 1, againsupported by the conducting fabric Zorflex®. The closed state wasinduced by application of a 1.20 volt bias for 120 seconds (see Theoryof IPN Electroactuation from Open to Closed State, above). Integrationof the traces indicates that the closed state is able to block 98.8% ofthe vapor that the open state allowed passage for, over a period of 15hours. Thus, an effective protective closed state demonstratingbistability for at least 15 hours was achieved in the relatively shortvoltage application time of two minutes. FIG. 25 compares vapor passagethrough the Zorflex® fabric alone, and passage through the IPN-fabricclosed state. Integration of both traces shows that the fabric aloneallows passage of 8.7-fold more vapor than the IPN-fabric closed state.This is a clear demonstration that the IPN alone provides most of theprotective characteristics of the composite. FIG. 26 shows vapor passagethrough the IPN-fabric closed state after 48 hours (red) and 7 days(black). Integration of the former shows that the composite stillretains a most of its protective ability after the passage of two days,blocking 98.6% of the vapor that was passed by the open state. After 7days, integration of the trace shows that it was able to block 92.0% ofthe vapor that was passed by the open state. Thus, the closed,protective state maintains at least 90% bistability for a period of oneweek after the first exposure to simulant. The bar graph in FIG. 27depicts a summary of the vapor amounts that that were passed by variousstates of the composite at four time intervals, and the empty gasket. Incan be seen that the closed state composite is able to provideprotection even after several challenges from the simulant.

Similar studies of the open and closed states were conducted with thecomparative IPN 2 and IPN 3. Polyester was used as the fabric supportfor the former, wool was used for the latter. The weight ratio of IPN tofabric was 1:1. The bar graph of FIG. 28 and Tables 1 and 2 demonstratethat IPN 1 has, by far, the most effective closed protective statecompared to IPNs 2 and 3. As Table 1 indicates, the ratio of simulantvapor permeation rates through the open vs. closed states is ˜10 to17-fold higher for IPN 1 vs. IPNs 2 and 3. This arises from the highlyeffective closed state afforded by IPN 1—Table 2 indicates that theclosed state of IPN 1 blocks the passage of between 6 and 13-fold moresimulant vapor than the closed states of IPNs 2 and 3. Vapor passagerates through the open state of IPN 1 is intermediate to those of IPNs 2and 3.

TABLE 1 Ratios of simulant permeation rates for the IPN - FabricComposites Ratio of Simulant Permeation Rates Open vs. Closed State IPN1 - 88.3 Fabric Composite IPN 2 - 8.16 Fabric Composite IPN 3 - 5.32Fabric Composite

TABLE 2 Ratios of simulant permeation rates for the IPN - FabricComposites Open State, Ratio of Closed State, Ratio of SimulantPermeation Simulant Permeation Rate vs. IPN 1- Rate vs. IPN 1 - FabricComposite Fabric Composite IPN 2 - 1.20 12.96 Fabric Composite IPN 3 -0.364 6.04 Fabric Composite

To summarize, for IPN 1 composite demonstrates an effective closed statethat is attainable using low to moderate voltages over relatively shorttimes, and its closed state is appears superior to those of the IPN 2and 3 composites synthesized previously.

For the composites to be effective and practical in chemical protection,they not only should demonstrate an effective closed state that isattainable using low to moderate voltages over relatively short times,but they also should demonstrate breathability in terms of high moisturevapor transport (MVT) rates. This is a requirement for the open state,and is desirable in the closed state also. MVT rates were measured byallowing water evaporation to occur through IPN-fabric composite samplesthat were mounted atop sealed vials containing water. Periodic weighingof the vial indicated weight losses that allowed calculation of the MTrates through the sample. FIG. 29 depicts a comparison between the threeIPN composites, in terms of MVT at 50% relative humidity and 37° C.Clearly, the IPN 1 composite shows superior MVTs, in both the open andclosed states. The MT for the open state is equivalent to commerciallyavailable sport clothing. It is a factor of ˜2 and ˜3 higher than thatof the IPN 2 and 3 composites, respectively. It is of interest that theclosed state MVT is superior to the open states of IPNs 1 and 2. Thusthe IPN 1 composite is the best performer of the three, in terms of bothchemical protection and breathability.

Further Embodiments

In the formation of IPN 1, increasing the amount of crosslinkersubstantially (from 7% to 20% or higher) resulted in a dense IPN networkthat is not able to be electrically actuated to a bistable closed stateusing moderate voltage levels (up to −2.5 volts). This version of IPN 1in the fabric composite with Zorflex, does however provide a largedegree of protection in its open state, and is very stable towardsrepeated simulant vapor challenges. FIG. 31 depicts the time-dependentsimulant vapor passage through this composite, which will be referred toas “highly crosslinked IPN 1-fabric composite”, or “HC—IPN 1-fabriccomposite”. It is seen that in its open state it blocks 98.5% of thesimulant vapor that passes through the standard IPN 1-fabric composite,over a time period of 200 minutes. The black and red traces representthe first and third vapor challenges the sample was subjected to. It isevident that the HC—IPN 1-fabric composite provides a very high degreeof protection when in its open state, and can withstand multiple vaporchallenges without a lessening of performance. FIG. 32 shows the MTrates that HC—IPN 1-fabric composite demonstrated, compared to thestandard IPN 1-fabric composite in its open and closed states, andZorflex® alone. At low relative humidity the HC—IPN 1-fabric compositeis able to support very high MVT, but at moderate relative humidity therate decreases to about one half of that of the standard IPN 1-fabriccomposite. Thus the open state of the former provides a large amount ofchemical protection, but with the tradeoff of having lower MT rates athigher relative humidity. Nonetheless, the HC—IPN 1-fabric composite maybe useful in certain protection applications, and it has the advantageof not requiring a power source for electroactuation to the closedstate.

In further studies it was found that use of higher voltages forelectroactuation (less than 10 volts) can in fact lead to closed statesfor these materials, and for other forms of the IPN that also have arelatively high density (data not shown).

Moreover, for related versions of the IPN one may envision (1)increasing the molecular weight of the conducting polymer chains, whichmay lead to a denser IPN structure, and/or (2) increasing the length ofthe charged tethers on the conducting polymer chain, which may lead tohigher MT rates. Also, other types of ionic liquids may be used, whichmay increase the composite conductivity or lessen the amount of powerrequired to transform the composite into its closed state.

Contemplated uses for IPN include protective garments (includingprotective masks, headgear, gloves, etc.), filters for gas and/orliquid, and shelters including temporary shelters.

Concluding Remarks

All documents mentioned herein are hereby incorporated by reference forthe purpose of disclosing and describing the particular materials andmethodologies for which the document was cited.

Although the present invention has been described in connection withpreferred embodiments thereof, it will be appreciated by those skilledin the art that additions, deletions, modifications, and substitutionsnot specifically described may be made without departing from the spiritand scope of the invention. Terminology used herein should not beconstrued as being “means-plus-function” language unless the term“means” is expressly used in association therewith.

REFERENCES

-   U.S. Pat. No. 8,940,173 B2, O. Bakajin et al, Jan. 27,    2015—“Membranes with Functionalized Carbon Nanotubes for Selective    Transport”.-   U.S. Pat. No. 9,095,821 B1, T. V. Ratto et al, Aug. 4,    2015—“Non-Reactive Process for Fixing Nanotubes in a Membrane in a    Through Passage Orientation”-   “An Elastomeric Poly(Thiophene-EDOT) Composite with a Dynamically    Variable Permeability Towards Organic Vapors,” B. D. Martin et al,    Adv. Funct. Mater. (2012) 22, 3116-3127.

What is claimed is:
 1. A fabric comprising a conductive polymercomprising poly(TP-CAE4P-SO3-co-bis-EDOT-co-HM-EDOT)poly((thiophene-3-carbonyl)-amino]-ethoxy}-ethoxy)-ethoxy]-ethoxy}-propane-1-sulfonate)-co-bis5,5 bis-3,4 ethylenedioxythiophene-co-hydroxymethyl-3,4ethylenedioxythiophene).
 2. The conductive polymer of claim 1, whereinsaid fabric is incorporated into a protective garment, a filter, or ashelter.